1. Field of the Invention
The present invention relates to a digital demodulator with a simple structure, which is capable of obtaining high quality demodulated signals.
2. Description of the Related Art
Digital FM demodulators are widely used in the fields of radio communications, particularly, in the field of mobile radio communications. As digital FM demodulators have more complex structures than analog FM demodulators, it is difficult to realize each digital FM demodulator by an integrated circuit (hereinafter called "IC"), a digital signal processor (hereinafter called "DSP") or the like. This is because the function of an ordinary digital FM demodulator needs complicated processing which involves trigonometric functions or is executed by a 90.degree. phase shifter, and thus requires large-capacity memory and vast amount of computations.
Digital FM demodulators which use a 90.degree. phase shifter are disclosed in, for example, U.S. Pat. No. 4,755,761 and Unexamined Japanese Patent Publication Nos. Sho 63-288504 and Hei 6-291553.
This type of digital FM demodulator suffers a difficulty in reproducing carriers and a difficulty in being designed into an IC because of the use of the 90.degree. phase shifter.